If your 2006-2009 Buick LaCrosse is suffering from harsh, unpredictable shifting or is stuck in limp mode, the problem is very likely a failing Transmission Control Module (TCM). As a technician with over two decades of experience, I’ve seen these symptoms countless times. This isn’t just an annoyance; it’s a critical failure that compromises your vehicle’s performance and safety. This OEM-quality T42 TCM, part number 24240400, is the definitive, reliable solution to restore your transmission’s smooth operation and your driving confidence.
The biggest challenge with replacing a TCM has always been the expensive and time-consuming trip to the dealership for programming. We eliminate that step entirely. We pre-program this module to your vehicle’s specific VIN before it ships, ensuring it’s ready for a true plug-and-play installation right out of the box. This saves you hundreds of dollars in dealer fees and gets your LaCrosse back on the road faster.
Case Study: A Tricky Diagnosis
A customer brought in their ’07 LaCrosse with a complaint of intermittent, violent 1-2 shifts and a persistent Check Engine Light. They’d already replaced two shift solenoids at another shop with no success. A quick scan showed a P0700 (Transmission Control System Malfunction) and a history of solenoid circuit codes. Based on my experience with these GM platforms, I suspected the root cause wasn’t the solenoids themselves, but the module commanding them. The internal drivers on these TCMs can weaken over time, causing erratic signals. We installed one of our VIN-programmed modules, and the problem was solved instantly. The car shifted like new, proving that replacing the brain, not just the parts it controls, was the correct fix.
Common Signs of a Failing LaCrosse TCM
A faulty TCM can manifest in several ways. If you’re experiencing any of the following, it’s time to consider a replacement:
- ✔ Harsh, banging shifts or delayed gear engagement.
- ✔ Vehicle is stuck in one gear (often 2nd or 3rd), also known as “limp mode.”
- ✔ The Check Engine Light or a transmission-specific warning light is illuminated.
- ✔ Diagnostic Trouble Codes (DTCs) are present, especially P0700, P0750, or other solenoid-related faults.
- ✔ Inability to upshift or downshift, leading to poor acceleration and fuel economy.
- ✔ Intermittent loss of communication with the module, causing unpredictable behavior.
Your Step-by-Step Installation Guide
For the 2006-2009 Buick LaCrosse, this is a job most DIYers can handle in their own garage in under 30 minutes. The module is conveniently located under the lower air cleaner housing.
- Safety First: Disconnect the negative terminal from your vehicle’s battery to prevent any electrical shorts and to help reset the vehicle’s adaptive memory.
- Access the Module: Remove the air cleaner assembly to gain clear access to the TCM mounted below it.
- Disconnect and Remove: Carefully unplug the electrical connectors from the old TCM. Then, unbolt the module from its mounting bracket and remove it from the vehicle.
- Install the New Module: Mount your new, pre-programmed TCM onto the bracket and securely fasten the bolts. Reconnect the electrical connectors, ensuring they click into place.
- Reassemble and Finalize: Reinstall the air cleaner assembly. Reconnect the battery terminal. Start the vehicle and let it idle for a few minutes. While not always necessary, using a basic scan tool to clear any stored DTCs is a good final step.
Guaranteed Fitment for Your Vehicle
This module is a direct-fit replacement for the 2006-2009 LaCrosse Transmission Control Module. It is also a compatible replacement for a wide range of other GM vehicles that use the T42 TCM, including models from Chevrolet, GMC, Pontiac, and Saturn. It interchanges with numerous part numbers such as 24252114, 24234503, 24239224, and 24240400, ensuring broad applicability and a reliable fix.
Frequently Asked Questions
Does this module really not need to be programmed by a dealer?
That’s correct. We handle all the programming here using your vehicle’s VIN. When you receive the part, it is fully configured for your specific LaCrosse and is ready for immediate installation without any additional steps.
What is a core charge? Do I need to send my old part back?
A core charge is a deposit you pay until you return your old part. We do not have a core charge on this item, so you can keep your old module without any penalty or hassle.
What kind of warranty comes with this part?
This transmission control module is backed by our one-year, hassle-free warranty, giving you peace of mind with your purchase.
Will this fix a P0700 code on my LaCrosse?
A P0700 code is a general fault code indicating the TCM has detected a problem. While this module often resolves the root cause (like a faulty internal driver that triggers other codes), you should always diagnose any other specific codes that accompany the P0700. In many cases, a failing TCM is the primary culprit.
Is the location mentioned (under the air cleaner) the same for all compatible vehicles?
No, the location varies by model. For the 2006-2009 Buick LaCrosse, it is under the lower air cleaner housing. For a Chevy Silverado, it might be next to the battery. Always verify the location for your specific vehicle, but the installation process remains similarly straightforward.